This disclosure is generally related to high speed wireless packet-based data networks and devices. In particular, this disclosure is related to devices that are at least capable of operating in fourth generation (“4G”) wireless networks. Examples of 4G wireless technologies include Worldwide Interoperability for Microwave Access (“WiMAX”) technologies and Long Term Evolution (LTE) technologies. 4G next-generation networks are characterized by reliance upon the Internet Protocol (IP) and packet-based signaling, along with improved uplink/downlink modulation coding schemes (MCS) and data rates.
International Mobile Telecommunications-2000 (IMT-2000), better known as “3G” or 3rd Generation, is a family of standards for wireless communications defined by the International Telecommunication Union, which includes GSM EDGE, UMTS, and CDMA2000, as well as DECT. Services include wide-area wireless voice telephone, video calls, and wireless data, all in a mobile environment. Compared to earlier 2G and 2.5G services, 3G allows simultaneous use of speech and data services and higher data rates (up to 14.4 Mbit/s on the downlink and 5.8 Mbit/s on the uplink with certain enhancements). Thus, 3G networks enable network operators to offer users a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency. Generally, 3G devices benefit from both a larger footprint coverage area, as well as national coverage.
International Mobile Telecommunications-Advanced (IMT Advanced), better known as “4G”, “4th Generation”, or “Beyond 3G”, is the next technological strategy in the field of wireless communications. A 4G system may upgrade existing communication networks and is expected to provide a comprehensive and secure IP based solution where facilities such as voice, data and streamed multimedia will be provided to users on an “anytime, anywhere” basis, and at much higher data rates compared to previous generations. 4G devices provide higher speed and increased Quality of Service (“QoS”) than their 3G counterpart devices. One 4G technology is WiMAX, a wireless system that adheres to the IEEE 802.16-2009 Air Interface for Fixed and Mobile Broadband Wireless Access System, which is the current updated “rollup” of 802.16-2004, 802.16-2004/Cor 1, 802.16e, 802.16f, 802.16g and P802.16i.
WiMAX systems present various traffic scheduling and QoS challenges. For example, the quality of the wireless channel is typically different for different users and randomly changes with time (on both slow and fast time scales). Further, wireless bandwidth is considered to be a scarce resource that needs to be used efficiently (i.e., you can not overprovision the wireless link). In addition, an excessive amount of interference and higher error rates are typically experienced. Scheduling decides the modulation coding scheme (MCS) and affects error rate, and error rate affects the choice of MCS. In general, mobility complicates resource allocation.
Another 4G system is “Long Term Evolution” (LTE), the project name of a high performance air interface for cellular mobile communication systems and is a step toward 4G radio technologies designed to increase the capacity and speed of mobile telephone networks. Where the current generation of mobile telecommunication networks are collectively known as 3G, LTE is marketed as 4G. However, it does not fully comply with the International Mobile Telecommunications (IMT) Advanced 4G requirements. Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE beginning in 2009. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) which is introduced in 3rd Generation Partnership Project (3GPP) Release 8, with further enhancements in Release 9. These enhancements focus on adopting 4G mobile communications technology, including an all-IP flat networking architecture.
The LTE standard includes: For every 20 MHz of spectrum, peak download rates of 326.4 Mbit/s for 4×4 antennas, and 172.8 Mbit/s for 2×2 antennas; Peak upload rates of 86.4 Mbit/s for every 20 MHz of spectrum using a single antenna; Five different terminal classes have been defined from a voice centric class up to a high end terminal that supports the peak data rates. All terminals will be able to process 20 MHz bandwidth; At least 200 active users in every 5 MHz cell. (Specifically, 200 active data clients); Sub-5 ms latency for small IP packets; Increased spectrum flexibility, with spectrum slices as small as 1.5 MHz (and as large as 20 MHz) supported; Optimal cell size of 5 km, 30 km sizes with reasonable performance, and up to 100 km cell sizes supported with acceptable performance; Co-existence with legacy standards; Support for MBSFN (Multicast Broadcast Single Frequency Network) which can deliver services such as Mobile TV using the LTE infrastructure, and is a competitor for DVB-H-based TV broadcast; and Per-User Unitary Rate Control (PU2RC), an advanced MIMO technique, i.e., a practical solution for MU-MIMO, which effectively utilizes multiuser precoding and scheduling to enhance the system performance of multiple antenna networks will be handled in a future release, i.e., LTE Release 10 and beyond (LTE-Advanced). A large amount of the LTE development work is aimed at simplifying the architecture of the LTE system, as it transits from the existing UMTS circuit-switched/packet switched combined network, to an all-IP flat architecture system.
LTE uses OFDM for the downlink—that is, from the base station to the terminal. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. OFDM is a well-established technology, for example in standards such as IEEE 802.11a/g, 802.16, HIPERLAN-2, DVB and DAB. In the LTE downlink, there are three main physical channels. The Physical Downlink Shared Channel (PDSCH) is used for all the data transmission, the Physical Multicast Channel (PMCH) is used for broadcast transmission using a Single Frequency Network, and the Physical Broadcast Channel (PBCH) is used to send most important system information within the cell. Supported modulation formats on the PDSCH are Quadrature Phase Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (QAM) and 64 QAM. For MIMO operation, a distinction is made between single user MIMO, for enhancing one user's data throughput, and multi user MIMO for enhancing the cell throughput.
In LTE's uplink, for the Physical Uplink Shared channel (PUSCH) only, LTE uses a pre-coded version of OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA). This is to compensate for a drawback with normal OFDM, which has a very high peak-to-average power ratio (PAPR). High PAPR requires expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and drains the mobile station's battery faster. In LTE's uplink, there are three physical channels. While the Physical Random Access Channel (PRACH) is only used for initial access and when the User Equipment (UE) or MS is not uplink synchronized, all the data is sent on the Physical Uplink Shared Channel (PUSCH). If there is no data to be transmitted on Uplink for a UE, control information would be transmitted on the Physical Uplink Control Channel (PUCCH). Supported modulation formats on the uplink data channel are QPSK, 16 QAM and 64 QAM.
WiMAX and LTE have many similar futures. For example, WiMAX utilizes a Channel Quality Information (CQI) (e.g., over a CQI channel—CQICH), throughput, CINR, and MIMO that are all present in LTE. One difference is in the naming convention used for MIMO in LTE. In LTE, downlink MIMO-A is called “downlink transmit diversity”, and MIMO-B, as it is defined in WiMAX, is called Multi-User-MIMO (MU-MIMO).
The SS can use a specific channel or a MAC message to transmit signal quality information periodically or when a specific condition is satisfied. For example, in WiMAX, the specific channel includes a CQI channel (CQICH), and the MAC message includes a REP-REQ/RSP MAC level management message.
In packet-switched circuits, “real-time” voice such as VoIP data, requires higher priority than other types of service flows to ensure adequate QoS. Conventional approaches do not optimize VoIP traffic. For example, in WiMAX, the CQICH is capacity-limited and cyclic, i.e., the physical maximum number of CQICH is 64 per frame. If all available CQI channels are fully occupied, then a CQI channel will not be able to be allocated until the next cycle is available. If the opportunity is missed, the MS has to wait for next cycle, e.g., every 2, 4, or 8 frames, depending upon the specific system implementation. An enhanced 6 bit CQI channel takes one slot from the UL subframe where one slot is 1 subchannel×3 symbols.
A BS can allocate a CQICH for a SS to an uplink and request downlink signal quality information from the SS. If a measured value of the downlink signal quality information transmitted from the terminal to the BS, the BS requests that the SS transmits downlink signal quality information via the CQICH channel.
In conventional WiMax, “Channel measurement Report Request” (REP-REQ) and “Channel measurement Report Response” (REP-RSP) (collectively, “REP-REQ/RSP”) MAC messages may be used on an as-needed basis, and may be triggered when a CQICH is not available for additional users. A REP-REQ message is used when a BS requests DL channel measurement results such as RSSI and CINR information for a SS. The REP-RSP message is used by the SS in order to respond to channel measurements listed in a received REP-REQ message, and the SS transmits a channel measurement report response message including measurement results of channels listed in a REP-REQ received. When transmitting signal quality information using a MAC management message, if downlink signal quality information transmitted from a SS to a BS is less than a reference value, the BS allocates radio uplink resources to the SS.
The conventional scheme is to use REP-REQ/RSP (or MAC level messaging) once the capacity limit of CQICH is reached. In other words, some active users may be using CQICH, while other active users are using REP-REQ/RSP. The problem of this conventional approach is that there is no consistency in Physical Carrier-to-Interference and Noise Ratio (PCINR) reporting among active users. Unavailability of a CQI channel results in the SS not being able to report either the physical (or effective) CINR to the BS.
CQICH and REP-REQ/RSP are defined in the IEEE 802.16 Standard. Some Radio Access Network (RAN) vendors use CQICH until the maximum number of users is reached, and then REP-REQ/RSP is used for any additional users. However, CQICH and REP-REQ/RSP are not conventionally known to be adaptively switched back and forth for the same user.
What is needed is a system and method for a wireless device to overcome CQICH capacity limitations and which allows active users to provide consistent PCINR reporting without limiting the CQI cycle. What is further needed is a system and method for a wireless communications system that allows user reporting through REP-RSP to be switched back to CQICH if CQICH later becomes available.